Hybrid materials composed of organic polymers coated with inorganic minerals have attracted much attention in biology and medicine due to their combination of advantageous properties. Polymeric materials can be a desirable base material for biomedical applications, as they can be processed into a variety of sizes and geometries, and can be designed to bioresorb in a controllable timeframe. Therefore, polymeric biomaterials have been featured in a variety of applications, including medical devices, tissue engineering scaffolds, and drug delivery systems.
Calcium phosphate based mineral coatings represent desirable surfaces for biomedical applications, as they can be similar in composition to bone tissue, and have been shown to promote favorable interactions with natural bone, a property termed “bioactivity”. For example, hydroxyapatite, the major inorganic component of bone mineral, is osteoconductive (Ducheyne et al., 1999), and may also be capable of inducing new bone formation in vivo (Habibovic et al., 2006).
A particular subset of approaches used to grow hydroxyapatite coatings on biomaterials surfaces mimics some aspects of natural biomineralization processes, and has therefore been termed “biomimetic” or “bioinspired” (Hong et al., 2006; Gao and Koumoto, 2005; Leveque et al., 2004; Green et al., 2006). This type of approach is a practically and economically attractive alternative to high-temperature commercial processing methods such as plasma-spraying (Gledhill et al., 2001), sputter coating (Yamashita et al., 1994), and laser deposition (Fernandez-Pradas et al., 1998). Kokubo et al. first reported bioinspired growth of apatite coatings on bioactive CaO—SiO2 glass in a simulated body fluid (SBF), which had ion concentrations nearly equal to those of human blood plasma and was held at physiologic temperature and pH (Kokubo et al., 1990). A series of subsequent studies reported mineral growth using novel formulations of SBF (Oyane et al., 2003), variation in the mineral growth process (Miyaji et al., 1999), or variations in the base materials (Yogogawa et al., 1997). The basis for mineral nucleation in these studies involved interactions of mineral ions in solution with polar functional groups on the materials surface, such as Si—OH (Li et al., 1992), Ti—OH (Barrere et al., 2004) and Zr—OH (Uchida et al., 2001). A series of recent studies has extended the bioinspired mineralization process to include formation of a bone-like hydroxyapatite coating on biodegradable polymer films (Murphy and Mooney, 2002) or porous scaffolds (Murphy et al., 2000; Zhang and Ma, 2004; Bajpai and Singh, 2007). The mechanism for mineral nucleation and growth on these materials is based on the interaction of carboxylate and hydroxyl groups on the hydrolyzed surface with calcium- and phosphate-rich nuclei in solution, creating a driving force for heterogeneous nucleation and mineral growth (Murphy and Mooney, 2002). This coating process is particularly suitable for biocompatible implants and biodegradable polymers, as it can be carried out at physiological temperature and pH (Tanahashi et al., 1994), and the mild processing conditions also suggest that it is possible to incorporate biologically active molecules such as polypeptides and polynucleotides, during the coating process.
Previous studies have shown that demineralized bone matrix (DBM) is an osteogenic material, but Ozturk et al. 2006 Int Orth. 30, 147-152, shows that DBM alone shows better osteoconductive properties than the DBM/hydroxyapatite (HA) mixture.